Lifetime and carrier-concentration profile of B⁺-implanted p-type HgCdTe

The lifetime and carrier-concentration profile of Hg_1-xCd _xTe photodiodes (x=0.2-0.3) formed by implantation of B⁺ ions (100 keV, 10¹³-10¹⁴ cm ^-2) into a p-type substrate was investigated. Using graded C-V measurements, concentration of carriers around the n⁺p junction was obtained. It was found that the junction is located at a depth of 0.7-1.5 μm, depending on the bulk hole concentration. The technique enables profiling of the same sample after annealing. The annealing process was shown to make the electron concentration shallower and thus to bring the junction closer to the surface. Various techniques were used to measure excess carrier lifetimes. All indicate that the extent of degradation of the excess electron lifetime in the p region is very limited. For all tested samples, an etch of 2 μm was enough to recover the bulk lifetime. These results contradict the general assumption of deep damages in the p-type substrate. Thus, the contribution of the n ⁺ side to the saturation current and to the R₀A product cannot be neglected.